In the field of biofuels production, it is desirable to efficiently convert biomass into usable fuels. Such biomass may consist of forest products or waste, terrestrial plants or crop wastes, or aquatic organisms. Fuel energy is available in such biomass because photosynthetic plants convert solar energy to stored carbohydrates, lipids, and proteins, which can then be burned directly or converted to fuels in other forms.
Various previous methods have been described for processing biomass into fuels using elevated temperature, pressure, catalyst, or all three. The reaction process can be operated under various conditions to yield various combustible gases, such as syngas (primarily carbon monoxide and hydrogen) or synthetic natural gas or SNG (primarily methane). Under still different conditions the product may be a liquid hydrocarbon.
In general, these processes use a dry feedstock. If, however, it is desired to use a feedstock with substantial water content, such as an aquatic biomass, then the process variables are different. For wet feedstocks, the pressure and temperature can often be selected to achieve acceptable yields of gas. In some cases, the necessary pressure and temperature can be lowered by the use of a catalyst. Various systems for the catalytic processing of wet biomass at reduced temperature and pressure have been previously described.
In the case of catalytic conversion of wet biomass, the fuel part of the gas is mostly methane, with a smaller amount of hydrogen and higher hydrocarbons. This mixture might be called “renewable natural gas” because the composition is essentially the same as commercially-delivered fossil natural gas. The remainder of the gas produced is typically non-combustible.